International Patent Application Publication Number WO 2008/010921 and International Patent Application Publication Number WO 2008/103949 disclose certain compounds that are reported to be useful to modify the pharmacokinetics of a co-administered drug, e.g. by inhibiting cytochrome P450 monooxygenase. One specific compound identified therein is a compound of formula I.

International Patent Application Publication Number WO 2010/115000 discloses methods for preparing the compound of formula I and salts thereof. Two intermediates discussed in these applications include the compound of formula II and the compound of formula III and salts thereof.

European Patent Application EP 486948 discloses a compound of formula IV′ and International Patent Application Publication Number WO 1994/14436 discloses a compound of formula V′.

There is currently a need for improved synthetic methods and intermediates that can be used to prepare the compound of formula I and salts thereof. There is also a need for improved methods and intermediates that can be used to prepare the compound of formula II and the compound of formula III which are useful for preparing the compound of formula I. The improved methods and intermediates may reduce the cost, time and/or the amount of waste or provide an increased yield associated with the existing methods for preparing the compounds of formula I or formula II or formula III or salts or protected derivatives thereof.